Apparatus for testing the embrittlement cracking characteristics of solutions



.mesas May 2e, i942 @finira naar erstes l APPARATUS FOR TESTENG .THEEml'll- 'ELEMENT CRACKING HARACTEBSTHCS OF SOLUTIONS resented bytheSecretary of his successors in omce Application october 12, 193e, seraiNo. 234,722

' (ci. 1e-.51)

(Granted under the act of March 3, 1883, as

amended April 30, 192%; 370 0. G. 757) 5 Claims.

The invention described herein may be manufactured and used by or forthe Government of the United States for governmental purposes only'without the paymentl of any royalty thereon.

'This invention relates to an apparatus for testing the embrittllng orintercrystalline cracking characteristics of water used in an operatingboiler or of solutions used in other metal vessels. I

Serious diiculties from embrittlement in boilers, digesters, etc., havebeen encountered and recognized for a number of years. Investigation hasclearly shown that dilute` alkaline solutions, such as used in boileroperation, will notcause embrittlement cracking.- .For example, water ina boiler will seldom c ntain more than a few thousand parts per mil ionof sodium hydroxide, and at such a degree of dilution, the watercannotcause embrittlement cracking of tube ends,

riveted seams, etc. In the laboratory, it has been found that from50,000 to 500,000 parts per million of sodium hydroxide are usuallynecessary to cause cracking.

Our investigations have shown that if a dilute boiler water, orsolution, is concentrated by evaporation it can produceembrittlementcracks and failures in steel which is maintained under stress in contactwith such concentrated solution. Concentration easily can beaccomplished by withdrawing a sample of water from the boiler andevaporating it until it contains from 200,000 to 500,000 parts permillion of sodium hydroxide. Such concentrated solution, heated to theatmospheric boiling temperature, or to a higher temperature underpressure, can be placed in contact with a stressed steel specimen, andif intercrystalline cracking results, the water is a dangerous one andmay cause embrittlement cracking in the boiler metal.

Concentration of the dilute water solution also can be produced directlyin contact with a stressed specimen instead of being concentrated andlater brought into contact with the specimen. A number of tests havebeen made with apparatus of this character wherein the dilute boilerWater has been placed in a receptacle` having a small space one wall ofwhich is formed by the stressed specimen to be tested, andthe device isplaced in a furnace or other heating equipment to be brought up to thetemperature the: interior and at which it is desired to conduct thetest. Steam thus generated is slowly bled 0E to permit concentration ofthe boiler water in the device, which is commonly known as a bomb Thesmall space referred to is usually annular and by making such spacequite narrow, itis possible to concentrate the boiler water manyhundredfold. The stress can be applied tothe specimen in any 4desiredmanner, either internally or externally,

and it may be provided before the test is started and/or at any timeduring the test.

If the initial sodium hydroxide concentration of the boiler water isknown, the nal concentration attained in the bomb can be determined bycondensing and measuring the steam which is driven ofi. The solution canbe maintained at any desired concentration by closing a bleed valve.

.Concentration of the dilute boiler water also can be secured withoutactually bleeding off steam from the device. For example, if a closedcontalner is provided with a depending hollow member in which thespecimen is arranged, and

whereinl small clearance is provided between the specimen and thedepending hollow member, heat may be applied to such member. conditions,steam will be generated in the small space adjacent the specimen and thesteam will pass upwardly into the receptacle, thus leaving aconcentrated solution in contact with the'specimen. As' in the previouscase, the specimen may be maintained under stress in any desired mannerto determine whether embrittlement cracking o f the metal will occur. f

In steam boiler operation, or in other metal vessels, embrittlementcrackingv is found in rivets, butt straps, drum sheets, tube ends, etc.,that are at the same temperature as the boiler water and therefore couldnot cause solution concentration by evaporation against the boilerpressure or evaporation in accordance with the test methodsreferred toabove. This obviously is true for the reason that the rivet heads andother elements referred to do not have sources of heat supply whichcould cause the evaporation. f

In the testing methods referred to above, concentration of the boilerwater or other solution requires that a specimen of the water be removedfrom the boiler or other vessel or isolated in a Under such y separatevessel attached to the boiler with suittions that produce cracking ineither of the test methods referred to are not necessarily the'same asthose that cause embrittlement of the metals comprising the parts orelements of the boiler or vessel. 1

An important object is to provide a novel apparatus for testing theembrittlement cracking characteristics of boiler wateror other solutionswherein actual operating conditions are reproduced.

l `A further object is to provide a novel apparatus of the characterreferred to wherein the Solution is led directly from the boiler orother vessel over a test specimen undervv conditions reproducing actualconditions within the Aboiler or other vessel whereby any changesoccurring in -the boiler will be reproduced during the practice of themethod and thus provide accurate information as to the characteristicsof the solution.

A further object is to provide a novel apparatus wherein water or othersolution from a lboiler or other vessel is led directly over a specimento be tested in a reduced restricted 'flow whereby concentration of thesolution will occur against the specimen to reproduce conditions whichare occurring within the seams or other restricted spaces in a boiler oron other metal surfaces in of the present invention4 other vessels atpoints where embrittlement' cracking usually occurs.

Al further object is to provide such an apparatus wherein evaporation ofthe solution takes place from the side of the specimen opposite that atwhich the solution is fed thereto to eiIect a tus wherein the normaloperating conditions in a boiler or the like are accurately reproducedso the present invention, therefore, water is led directly from theboiler or other vessel into the testing device and -a flow of the wateris provided at a slow rate through a restricted space one `wall of whichis formed by the test specimen. approximate boiler temperature beingmaintained atthe test point to assist in simulating or reproducing'actual conditions at points within a boiler or the like whereembrittlement cracking takes place. During passage through therestricted space pressure is released and steam escapes toward theatmosphere through an loutlet pipe preferably controlled by a bleedvalve whereby the rate of flow of the escaping fluid canv be controlled,such iiuid, of course. being in the form of steam developing incident tothe releasing of the pressure.

The rate-at which pressure is released by per- Y mitting the escape ofsteam, together with vthe restriction ofthe space throughwhich thesolution ows past the speciment'will determine the rate of ilow of thesolution past the specimen, and accordingly any desired rate ofconcentration adjacent to the specimen can be provided. This restrictedspace, as indicated above, constitutes a simulation of conditions thatexist in a riveted seam or rolled in tube end or other place in a boilerin which embrittlement cracking is commonly encountered. As vthe boilerwater passes through the seam or rolled in tube end it 'progressestoward a region of lower or atmospheric pressure and therefore due toits high temperature this drop in pressure causes the escape of steamtoward the atmosphere and the consequent concentration of the solutionremaining in the-restrictedpassage. :The conditions created in theequipment described in this inthat the results obtained by the apparatusare accurate indications of the embrittlement characteristics of thesolution inthe boiler or the like.

A further object is to -provide an apparatus yhaving a restrictedpassage for the iiow of boiler water or the like directly from theboiler or other vessel and wherein a specimen under stress forms onewall of the restricted passage, and wherein evaporation of the solutionand the concentration thereof will occur in contact with then specimento reproduce conditions within the boiler or other vessel.

A further object is to provide a novel apparatus of the character justreferred to wherein evaporation is caused to take place at the end ofthe restricted passage opposite the end to which the solution isintroduced to facilitate the concentration of the solution in contactwith the specimen.

Other objects and advantages of the invention will become apparentduring the course of the following description.

We have discovered that the conditions under which embrittlementcracking occurs in boilers or other vessels may be closely simulated orexactly reproduced so as to render a test device of this generalcharacter far more accurate and vention duplicate these conditionsexisting in4 the riveted seams or rolled in tubes' or other restrictedspaces in the boiler.

The specimen being tested obviously is maintained under stress duringthe test,' and the stress may be internal and/or external, and it may beapplied before or'during the test and 4;,- maintainegl throughout thetest. It will be apparent therefore that the test exactly duplicates theconditions that cause embrittlement of the rivets, butt straps, etc.,and'can be operated con- .4 tinuously on the boiler or vessel sothat'any change which creates a dangerous condition in the water will beimmediately discovered. With dependable in its results. In accordancewith 76 the proper instructions, the test can be conducted withoutspecialskill or training, and complete control is provided overthegoperation of the equipment. In waters or solutions that are treatedto render them incapable of producing embrittlement cracks, the testobviously` can be used to estimate the eil'ectiveness of the treatmentemployed.

have indicated .that the solution from a steam boiler or other vesselmay be very easily concentrated to produce embrittlement cracking byallowing it to leak or diffuse through a small .opening more slowly thanit is permitted to evaporate on the other side' of the leak or openingby protviding the steam escape control means referred In the drawing wehave shown several types of apparatus particularly adapted forpracticing the method. In this showing,

Figure 1 is a sectional view showing one type of apparatus wherein thespecimen is spring loaded to be maintained under stress,

Figure 2 is a similar view of a modified form Somewhat more specically;our experiments 2,283,954 .tot theinvention wherein the spring loadingis transmitted to the specimen longitudinally thereof and issupplemented by lateral .stressing means,

Figure 3 is a similar View showing another modification wherein asubstantially cylindrical specimen is maintained under stress by beingdriven into position on a plug or the like, and,

Figure i is a similar view of afurther modiflcation wherein a conicalstretcher is employed -or the specimen and wherein the ow space pates areceptacle shown in the present instance as in the forni of a cast bodyhaving a passage il therethrough into one end of which is thread-l ed apipe i2 connected to the boiler or other receptacle to feed directlytherefrom the water or other solution to betested. A pipe I3 isthreadedin the other end of the body w and is provided with a take-od'pipe It preferably provided with a control valve le, and the pipe lepreferably leads to a suitable condenser.

Between the adjacent ends of the pipes l2 and i3 a test specimenindicated as a whole by the numeral it is arranged within the passageli,.

the space Il surrounding the specimen constituting a solutionconcentrating chamber, as will become apparent., The specimen is hollow,as shown and is provided at its lower end with an A annular flange i8forming a restricted annular 'passage it for the iiow-of water. Theupper end of the flange ld engages lugs 2d, extending intoV the bore il,to limit upward movement of the specimen. The specimen is providedintermediate its ends with a relatively thin cylindrical wall 2l at somepoint along which the embrittlement cracking is adapted to occur.

The specimen is provided at its upper end with a head 22 through whichextends a stem 23 having a head 2d at its lower end engaging the lowerface of the head 22 to exert an upward force for maintaining thespecimen under stress, as will become apparent. The stem 23 extendsthrough a plug 25 mounted in the upper endv of the pipe i3. A springseat 25 surrounds the stem 23 at a point spaced from the plug 25, andarelatively heavy compression loading spring 2l surrounds the stern 23between the plug 25 and spring seat 26. A thrust bearing 2B ispreferably arranged above and in engagement with the spring seat 2d, anda n ut 23 is threaded on the upper end of the stem 23. The upperextremity of the stem 23 may be formed polygonal as at et for engagementwith a wrench to prevent turning movement of the stem 23 while the nut29 is being turned.

A particularly advantageous form of the invention is shown in Figure 2wherein the speci- :men is subjected to both axial and transversestresses. A body 3l is provided with a chamber 32, and a cap 33 in thelower end of the body is tapped as at 34 for connection with a pipeleading to the boiler to supply boiler water lto the chamber 32. Thebody 3l also may be provided with an opening 35, connected to theboiler,

'l threaded at its upper end as at l2 for a purv pose to be described'.The stem il! extends downwardly through the upper end of the body 3| andis provided with a reduced test portion 3 withinthe space 36. Below thevtest portion the specimen is provided lwith a. conical portion 4d for atleastv partially closing the seat 33. Below the conical portion 4t thespecimen is provided with a depending cylindrical portion d5. A suitablepacking gland dB may be provided to prevent lealrage pastthe stem l Thebody 3l yis provided near one side-with a threaded opening for thereception of a plug il in which is arranged a stem da, this stem beingprovided with a threaded portion de engaging a similarly threadedopening in the plug al. The

inner end 5t of the stem a is engageable against the lower end a5 of thespecimen and it will be apparent that upon the application of a wrenchto the polygonal outer end 5l of the stem ed, the latter may be turnedin the plug lll to cause the inner end 5!) ofthe stem to exert a lateralforce against the lower end t5 of the specimen. The

stem t8 may extend through a suitable packingv gland 52 carried by theplug el.

A supporting sleeve 53 has its lower end threaded on an axial extension54 carried by the body 3i, and the upper end of the sleeve 53 carries aspring seat 35. A stem 56 has its lower end extending into the sleeve 53and enlarged as at 5l to receive the threaded upper-end d2 of tension ofthe spring 59. The upper end of the stem 56 may be made polygonal as at62 to be engaged by a wrench.l and thus hold the stem 5B against turningwhile the nut t! is being adjusted. It will become apparent that thespring 59 exerts an upward force on the stem 56 to maintain the specimenunder a static tensile load.

whereby a circulation may be maintained through thin substantiallycylindrical specimen 'l2 which ln`the form of the invention shown inFigure 3 a body S3 is provided with a passage 64 into the lower end ofwhich is tapped a pipe t5 to supply Water from the boiler or othernozzle. A cap member 6 5 is threaded in the upper end oi the bore and isprovided with a steam escape pipe 6l. This pipe also may be providedwitha control valve 68 and may lead to a suitable condenser. A specimensupport 69, in the form of a substantially cylindrical plug, issupported in the passage 64 by lugs l0 and may be held in the positionshown in Figure by a suitable spring The plug 69 is surrounded by arelatively is driven into position on the plug 69 to be thus maintainedunder substantial tension. The passage M forms a chamber 13 within thebody B3 and the lower end of this chamber is defined by the relativelynarrow annular space 'M surrounding the specimen 'I2 and forming asolution coni centrating space, as will become apparent.

threaded a stem 80 having a conical head 8| at one end. A specimen 82 isformed oi' relatively 'thin steel and coincides in shape and size to theconical head 8| to surround the latter. 'I'he smaller end of the head 8|is threaded as at 83 to receive a nut 84, whereby the specimen 82 may be,forced toward the larger end of the head 8| to be placed under staticcircumferentialtension. Between the head 8| and the plug `18, the bodyis ported as at 85 Vfor connection with a pipe 86 which may lead to aconventional condenser.

spaces of slow flow within 'a boiler at which V points embrittlementcracking usually takes place. l

in the annular space around the test portion '2| of the specimen. Eithersteam or a solution more dilute than that entering through the pipe I2must be taken off through` the pipe I4. In a test equipment, the devicehas been connected to a pressure vessel containing 2,000 parts permillion of sodium hydroxide at 200 lb. gage pressure, and it waspossible to tap off almost pure steam through the'pipe I4 and leave 0.3gram of sodium hydroxide in the annular space surroundingthe testportion of the specimen. The actual sodium hydroxide concentrationreached in such space was greater than 500,000 parts per million.

The form of the invention illustrated in Figure 2 is quite similar tothat shown in Figure 1 except ythat the specimen is of a dierent typeand is subjected both to axial and transverse stresses.

After the spring 58 has been provided with a predetermined loading,which obviouly will hold the conical element I4 on the seat 31 to act as4a valve therea'gainst, the stem 48 may be turned Pressure is releasedby opening the valve I5 to the proper extent. in which case the boilerwater is converted into steam at a rate'depending upon the degree ofopening of the valve I5. This action causes concentration of thesolution in the space around the test portion of the specimen. It willbe apparent that the space around the annular shoulder I8 is somewhatexaggerated and in actual practice only a slight leakage 'is provided sothat there will be an extremely slow flow of solution into the chamberI1.

The spring 21 is relatively heavy and its tension is adjusted by turningthe nut 28, preferably while engaging the polygonal head with a wrenchto prevent the turning of the stem 23. It will be apparent that thespring- 21 exerts an upward force on the upper end of the'specimen whilethe lower end of the latter is engaged by the lugs 20 to prevent itsupward movement. Accordingly the spring 21 acts to maintain any 'desiredstatic tensile load on the specimen.

As is true in all forms of the invention shown,

' the device in Figure 1 meets the essential requirement thatself-evaporation in theL boiler water or other solution takes placewhile in contact with the stressed specimen. The device operates byallowing leakage or diffusion of the solution through a small openingprovided around the flange I8 more slowly than evaporation takes placeon thelother side of the leak, and accordingly self-evaporation takesplace in contact with the specimen, as stated. It will be apparent thatthe connection of the device with the boiler or other vessel renders thedevice sensitive to any changes which take place in the source` of thesolution, and the heat of the source is main-- 'tained as well as thepressure in the source except for the slight drop in pressure occurringincident to the opening of the valve I5. vIt will apparent that after aperiod of time concentration takes place in contact with the'specimen inthe same manner that it takes place adjacent to the metal or parts inthe boiler which are usually subject to embrittlement cracking, and ifsuch cracking of the specimen takes place, the solution may be dangerousfor use in a boiler.

The leakage which takes place 'around the flange I8 must be slow enoughso that the solution canevaporate and deposit its dissolved solidinwardly to exert a lateral force against the lower end 45v of thespecimen.x 'I'his operation provides a lateral stress against thespecimen and also suiiiciently unseats the conical member M at the sideadjacent the stem I8 to 'permit a leakage between the chamber 32 and`the concentrating 'space 36.

The pipe 39, of course, `will be valve controlled to determine the rateof exhaustion of steam from the space 36 and consequently the rate ofevaporation therein. Concentration of the solution in the space 36,therefore, renders the device in Figure 2 similar in this respect to theoperation of the device shown in Figure l. Themechanism shown in Figure2 is advantageous in that it provides the two different stressesreferred to and for the additional reason thatit provides communicationthrough two openings (34 and 35) with the boiler or other vessel tomaintain a circulation through the chamber 32 so that the solutiontherein will always correspond to the solution in the boiler or othervessel regardless of any changes which take place therein. Accordinglythe device closely simulates or reproduces conditions .in the boiler orvessel. As in the form previously described, embrittlement cracking ofthe specimen indicates that the use of the solution is dangerous. Inboth of the forms of the invention described, breakage of the specimenis immediately visually indicated by the releasing of the stem 23 or 56by the springs acting upwardly thereagainst.

The form of the invention shown in Figure 3 is simpler than the formdescribed but provides no visible indication of breakage of thespecimen. `Very slow leakage takes place around the lower end of theplug 69, the space through which this leakage takes place beingexaggerated in Figure 3. Leakage of steam through the pipe 61 iscontrolled to determine the rate of concentration of the solution incontact with the specimen. The plug 69 and specimen are substantiallycylindrical and the specimen is driven into position to be placed undera static circumferential stress.

The form of the invention shown in Figure 4 provides the same result asin Figure 3, the speci- `men being p laced under circumferential stressvby tightening the nut 84 to force the specimen toward the larger end ofthe head 8| and thus tend to stretch it. The forms of the device shownin Figures 3 and 4, as in the previous cases, are adapted to beconnected to the boiler or other vessel, and the device in'Figure 4 isinitially Figure 3, provides a flow of solution past the specimen at arate slower than the rate of evaporation of the solution in contact withthe specimen whereby self-concentration of the solution takes place incontact with, thaspecimen.

From the foregoing it will be apparent that the can carry in contactwith a given solution.

present invention provides ajtest bombrfor determining the embrittlementcracking characteristics of boiler Water and other solutions, thetesting taking place under conditions closely approximating conditionswithin the seams, rolled in tube ends or other restricted spaces in theboiler or other vessel. The direct feeding of boiler water to eitherform-of the device insures the testing under temperature conditions'approximating those of the boiler, and the slow,

leakage provided through the valves I5 etc. maintain pressure in thedevice notgreatly below the pressure 'in the boiler or the like, thuslikewise closely reproducing pressure conditions .in the boiler duringthe testing operation. The form of the'device shown in Figure 2 isparticularly advantageous for the reason that it provides-stresses orfother methods of manufacture. Applied.

stresses may be createdby any applied load, sta-tic and/or fatigue,etc., or there may be a combination of internal and applied stresses.The essential requirement of the invention, as indicated above, is thatthe equipment must provide selfevaporation of the solution in contactwith the stressed specimen. f

The present invention, therefore, contemplates the reproduction incontact with a stressed specimen of conditions which exist in the boileror vessel or in restricted spaces therein in which the solution is beingemployed. More specifically, the'invention contemplates the slow leakingor diffusingA of the solution from the vessel through a constriction,and removing steam or vapor at the low pressure side of the constrictioncontaining a lower concentration of dissolved solid than the enteringliquid. In other words, the invention contemplates the maintenance of aslow flow of solution over a test specimen, such flow being at a rateslower than the rate of evaporation on the side of the specimen oppositethat through which tlie solution is introduced.' The steam or vapor maybe removed under atmospheric pressure or above or below atmosphericpressure.

The various forms of the device illustrated are preferably directlyattached to a boiler or other vessel and the forms of the inventionshown in ,Figures 1 and 2 will automatically warn the operator when thewater becomes dangerous and tends to cause embrittlement cracking. Thedevice is particularly advantageous for use in'determining the amount ofa chemical tobe added other end of said another passage at a greaterother vessel, of means for testing the embrittleof said passage, meansforrsupplying solution to sage, means for supporting and maintaining un-Aother end of said another passage to concentrate crackingcharacteristics of a solution, compristo boiler water or other /solutionto prevent embrittlement cracking. The device also is particularlyuseful in determining the embrittlement cracking characteristics of anyparticular steel or metal alloy. Obviously the device will Iallow thedetermination of the total safe load a given metal 'It is to beunderstood that the forms of the apparatus illustrated and described areto be taken vas preferred examples of the same, and that various changesin the shape, size and arrangement of parts of the apparatus may be madewithout departing from the spiritof the invention or the scope of thesubioined claims.

We claim:

1. Apparatus for testing the embrittlement cracking characteristics of asolution, comprising,r a body having a passage therein, means forsupporting and maintaining under stress a test specimen arranged withinand intermediate the ends be tested'to one end of said passage, andmeans for evaporating solution from the other end of said passage toconcentrate the solution in contact with the specimen.

2. Apparatusfor testing the embrittlement cracking characteristics of asolution. comprising a body having a passage therein, means forsupporting and maintaining under stress a test specimen arranged withinand intermediate the ends of said passage, means for supplying solutionto be tested to one end of said passage, means for restricting the ilowof solution from said last named means through said passage, and meansfor` evaporating solution from the other end of said passage at a rategreater than the rate of ow of the solution to said passage`toconcentrate the solution in contact with the specimen.

3. Apparatus for testing the embrittlement cracking characteristics of asolution, comprising means providing one passage for substantially freeand continuous circulation of solution from a body of solution to betested into one end and through said passage and from the other endthereof back to said body of solution to be tested, means providinganother passage for receiving solution at one end thereof from said onepasder stress a test specimen arranged within and intermediate the endsof said another passage, and means for evaporating solution from the thesolution in contact with the specimen.

4. Apparatus for testing the embrittlement ing means provided onepassage for substantially free and continuous circulation of Solutionfrom a body solution to be tested Iinto one end'and through said passageand from the other end thereof back to said body of solution to betested, means providing another passage for receiving solution at oneend thereof from said one passage, means for supporting and maintainingunder stress a test specimen arranged within and` intermediate the endsof said another passage, means for restricting the ow of solution fromsaid one passage through .said another passage, and means forevaporating solution from the rate than the rate of flow of solution tosaid another passage to concentrate the solution in contact with thespecimen.

5. The combination with a steam boiler or ment cracking'characteristicsof the solution in the vessel, comprising a body having a passagetherein, means providing another passage for substantially free andcontinuous circulation of solution from said vessel to the passage insaid body and from the latter passage to said vessel, means forsupporting a specimen in the passage

